(Meth)acrylic acid is generally produced by carrying out a gas-phase catalytic oxidation reaction to obtain a gas containing (meth)acrylic acid, supplying the gas into a condensation column or a collection column to obtain a crude (meth)acrylic acid solution, and purifying (meth)acrylic acid from the crude solution. The procedure for such a purification is exemplified by crystallization in addition to distillation, diffusion, extraction and others.
In general, crystallization of (meth)acrylic acid from a crude solution is carried out in two stages. First, (meth)acrylic acid is crystallized by cooling and the liquid portion is removed. Next, the obtained (meth)acrylic acid crystal is melted to be transported to the next step. In order to further improve the purity of a crystal, a sweating step may be carried out before the melting step in some cases. In the sweating step, the impurity which is present mainly in the surface area is removed by partially melting the crystal. As described in the above, in the purification by crystallization, both of cold energy for crystallizing (meth)acrylic acid and heat energy for melting the obtained crystal are required.
A refrigerator is employed for generating both of cold energy and heat energy. As a refrigerator, there are various types such as an absorption type refrigerator and a compression type refrigerator.
In an absorption type refrigerator, a liquid refrigerant for a refrigerator is evaporated to obtain vaporization heat and a cooling medium is cooled using the vaporization heat. The cooled cooling medium is provided to the outside.
The vaporized refrigerant for a refrigerator is absorbed in an absorbing liquid and then a refrigerant gas is separated from the solution in a rectification column or the like. The obtained refrigerant gas for a refrigerator is condensed to be devolatilized again, and a heating medium is heated by the condensation heat generated at the time and the heated heating medium is supplied to the outside. In a compression type refrigerator, a refrigerant gas for a refrigerator is directly compressed to obtain condensation heat without using an absorption liquid for absorbing or regenerating the refrigerant gas for a refrigerator. In any cases, a refrigerator can efficiently supply both of a cooling medium and a heating medium by repeating vaporization and devolatilization of a refrigerant for a refrigerator.
As described above, a refrigerator which can generate cold energy and heat energy is generally used in the crystallization purification of (meth)acrylic acid, since both of cold energy and heat energy are needed. Therefore, a method for efficiently producing (meth)acrylic acid using a refrigerator has been developed.
For example, Patent Document 1 discloses a method for producing an organic acid such as (meth)acrylic acid, wherein reaction heat and combustion heat of waste are recovered to be used as a heat source for an absorption type refrigerator. According to the method, the energy which has been discarded can be utilized effectively and thus it is made possible to save the product cost.